1. Field of the Invention
The invention relates to an airbag initiator which includes a squib for electrically igniting an explosive composition.
2. Description of Related Art
Various initiators are known in the art for electrically exploding an ignitable explosive composition ("charge"). For instance, FIG. 1 shows a conventional initiator 100 which includes casing 101, lead pins 102, 103, header 104, glass seal 105, ceramic chip 106, charge holder 107, first charge 108, air gap 109, second charge 110, cup 111 and insulating liner 112 inside cup 111.
FIG. 2 shows an initiator disclosed in U.S. Pat. No. 5,099,762 ("the '762 patent"). The initiator 200 includes casing 201, a pair of terminal pins 202, 203, bridgewire 204 connected between terminal pin 202 and header 205. Header 205 is also connected to the other terminal pin 203. The '762 patent discloses that the casing contains ignition charge 206 adjacent the bridgewire and output charge 207 which is adjacent to but axially spaced from the ignition charge. According to the '762 patent, the bridgewire is sandwiched between ceramic chip 208 and the ignition charge and glass seal 209 is adjacent the ceramic chip. The ceramic chip and the glass seal are located in a bore through the header and lead pin 202 is centered in the bore. RF attenuating means 210 surrounds the lead pins and splices 211, 212 connect the lead pins to leads 213, 214.
Conventional initiators typically utilize an arrangement of parts wherein a spark gap is provided, a lead pin is centered in a bore extending through a header, the bore in the header includes a ceramic heat sink sandwiched between the charge and a glass-to-metal seal, the charge includes two or more explosive compositions in contact with each other or separated by an air gap therebetween, and/or the charge is located within a cap which does not press the charge against the bridgewire. Such arrangements present various drawbacks.
In arrangements which have a lead pin centered in a bore through the header, it is necessary to change the header design to accommodate bridgewires of different lengths thus requiring the expense of separate designs, manufacture and assembly of such different header designs. Accordingly, there is a need in the art for an initiator wherein the same header design can accommodate bridgewires having different lengths.
In arrangements in which the cup of the squib does not press the charge against the bridgewire, there is the danger of misfiring due to inadequate contact between the bridgewire and the charge. Accordingly, there is a need in the art for an initiator design which provides constant pressure on the loaded powder charge to maintain contact of the charge and bridgewire after assembly operations, shipment and installation of the igniter in an air bag system.
In arrangements which use a ceramic heat sink, the provision of such a part and assembly thereof add to the cost of manufacturing the igniter. In order to produce a more economical igniter, it would be desirable to eliminate as many assembly operations as possible and construct the igniter with as few parts as possible. Thus, an igniter which includes fewer parts, such as an igniter without a ceramic heat sink should be more economical to produce.